Recently, owing to the advancement of technologies related to the multimedia, new technologies are rapidly spreading about the device and method of compressing and encoding audio data and video data, and processing of digital data produced by compressing and encoding. In particular, the capacity is rapidly becoming larger in recording media such as hard disk, optical disk, and memory card as recording media used in information appliances. Along with the trend of larger capacity of such recording media, in the field of consumer video appliance field, it is generally required to record video and audio signals for a long time such as movie programs in digital system. Further, by utilizing such digital recording technology of recording in digital system, as compared with recording by conventional analog system, movie programs can be recorded while maintaining high image quality and high sound quality.
On the other hand, by utilizing such digital recording technology, moving images and sound signals can be easily copied without deteriorating the picture quality or sound quality. Hence, copyrighted contents can be easily duplicated, and it was a conventional problem to prevent illegal copies. To solve such problem, hitherto, a technology has been proposed about copyright protection for the purpose of preventing illegal copies. One of the technologies about copyright protection is a technology of encrypting the information and encrypting the recording and communications in order to conceal the information in recording and communications. Accordingly, in recording media such as DVD as a kind of optical disk, or SD memory card as a kind of memory card, it has been proposed to record while the stream data including digital moving images and contents data are being encrypted. By such technology, the contents are concealed, and the copyright of the contents is protected.
A recording and reproducing apparatus for recording stream data including video data and others in such recording media, or reproducing the stream data recorded in the recording media is provided with LSI and other integrated circuits as the data processing units for compressing, expanding or encrypting the contents data. Further, for such data processing, usually, the outside of the LSI is provided with an external memory for temporarily storing the data being processed.
In such structure in which the LSI and external memory are connected and the data is processed, the image data to be encrypted and decrypted by, for example, the LSI, and the data in the process of decryption are transferred between the LSI and the external memory. Accordingly, it was possible to read, illegally, the data to be transferred to the external memory. On the other hand, by processing the data by making use of only the internal memory provided in the LSI, such illegal action can be prevented, but there was a limit for processing the large capacity of data such as image data by the internal memory alone. Hence, conventionally, it has been proposed to prevent illegal data reading while processing the data by using the external memory.
FIG. 7 is a block diagram of a conventional data processing device intended to protect the data. As shown in FIG. 7, the conventional data processing device reads the stream data recorded in a recording medium outside of the device such as DVD or memory card from recording medium interface unit (or called recording medium I/F unit) 910. Further, in the conventional data processing device, while the data being processed is stored temporarily in external memory 920, LSI 900 executes the data processing. In an example of the data processing device shown in FIG. 7, recording medium I/F unit 910 reads in the scrambled data recorded in the recording medium. The scrambled data is the image data being compressed and encoded into stream data by MPEG (Moving Picture Expert Group) system, and further processed by scrambling. LSI 900 executes a reproduction process of restoring the contents data of video and audio from such scrambled data.
When the scrambled data is supplied into LSI 900, descrambling unit 91 descrambles the scrambled data. As a result, descrambling unit 91 generates stream data based on the MPEG system, and transfers the stream data to internal memory 94 by internal CPU 90. The stream data transferred in internal memory 94 is transferred to external memory 920 by memory control unit 95, and is temporarily stored in external memory 920.
In such transfer of stream data into external memory 920, memory control unit 95 sets address data showing the transfer destination region of external memory 920, and supplied into external memory 920. Data type detection unit 96 detects the type information, that is, the information showing the frame type or the like, from internal CPU 90, and determines the correspondence between the stream data depending on the type information and the address of external memory 920 for storing the stream data. When the type information detected by data type detection unit 96 shows an I-frame, execution control unit 97 instructs encrypting unit 98 to encrypt the data. In response, encrypting unit 98 encrypts the stream data being transferred from internal memory 94 to external memory 920 by means of memory control unit 95. The encrypted stream data is stored in a storage region in external memory 920 indicated by the address data. On the other hand, when the type information detected by data type detection unit 96 shows other frame than I-frame, execution control unit 97 instructs encrypting unit 98 not to encrypt. In this case, the stream data stored in internal memory 94 is directly transferred to external memory 920 by passing through encrypting unit 98.
When the stream data transferred to external memory 920 is further transferred to internal memory 94, as required, the data is decrypted by decrypting unit 99. That is, when reading in the stream data from external memory 920, data type detection unit 96 detects the type information showing the type of each corresponding frame, based on the address data being read in by memory control unit 95. When the type information detected by data type detection unit 96 shows an I-frame, execution control unit 97 instructs decrypting unit 99 to decrypt the data, and decrypting unit 99 decrypts the stream data being read in. On the other hand, when the type information shows other frame than I-frame, execution control unit 97 instructs decrypting unit 99 so as not execute decrypting process, and the stream data being read in is directly transferred to internal memory 94 by passing through decrypting unit 99.
The stream data thus transferred to internal memory 94 is decoded by decoder 92, and the contents data of video and audio are restored. The restored contents data are delivered from output unit 93.
The conventional data processing device shown in FIG. 7 encrypts and decrypts the data transferred between external memory 920 and LSI 900, partially depending on the detection output of data type detection unit 96. Accordingly, in the conventional data processing device, the encrypting and decrypting load, that is, the data processing quantity can be curtailed as compared with the method of encrypting and decrypting all of transfer data. Also, in the conventional data processing device, in the stream data by the MPEG system, unless the image data corresponding to I-frame is decoded, image data corresponding to other frame cannot be decoded, and the confidentiality of image data is assured. That is, out of the stream data transferred between internal memory 94 of LSI 900 and external memory 920, only the stream data corresponding to I-frame is encrypted, and the confidentiality of image data in the data processing device using external memory 920 can be assured.
However, in the conventional data processing device, in data transfer between LSI 900 and external memory 920, encrypting unit 98 and decrypting unit 99 are needed, and the hardware quantity is increased. Further, in the conventional data processing device, although encrypting and decrypting processes are partial, the required processing load and transfer time are increased. In addition, to detect whether the stream data to be transferred to external memory 920 is I-frame or not, data type detection unit 96 and execution control unit 97 for changing over control of encrypting unit 98 and decrypting unit 99 are additionally needed. As a result, the hardware quantity is further increased, and the process for such control is complicated. In particular, as compressing and encoding techniques, since different standards are proposed such as MPEG-2, MPEG-4, or H.264, to handle stream data conforming to different standards, the process for detecting the data type is further complicated.
As described herein, by processing the copyrighted contents data by using only the internal memory provided in the LSI, illegal data reading can be prevented without using data type detection unit 96 used in the conventional data processing device. However, the required capacity of the internal memory is increased in order to process the image data of huge capacity only by the internal memory.